A secure recharge scheme for blockchain payment channels

Abstract

The payment channel is a prominent solution to scale the throughput of decentralized blockchain ledgers. It reduces the load on-chain by enabling off-chain micropayments without exhausting blockchain resources. However, the balance of a channel could become depleted due to payments going in one direction, making subsequent payments in that direction impossible. Several solutions have been proposed in recent years to address this issue. Nevertheless, ensuring both privacy and efficiency while maintaining applicability to edge nodes remains a challenging task. In this paper, we present PCRECHARGE, a solution to revive a depleted payment channel. Its key idea is to recharge the channel by conducting an on-chain payment and a reverse off-chain payment. The main challenge of this solution is to ensure that both payments must be performed atomically. To address this challenge, we conceive a pay-or-refund mechanism and integrate it into PCRECHARGE. It introduces another two transactions pay and refund, enabling an honest party to publish one of them to get his coins back. The most prominent feature of this mechanism lies in its independence from specific scripting and its avoidance of costly cryptographic tools, making it suitable for wide deployment. We provide comprehensive analyses and experimental evaluations to demonstrate the security and high efficiency of PCRECHARGE. Compared to reconstructing a channel, our approach reduces the transaction size by 66% in the honest case and addresses the limitations of current solutions, particularly their poor application to edge nodes.